With the recent popularization of portable electronics such as cellular phones, notebook-sized personal computers and video camcorders as well as vehicles such as hybrid electric cars, there is a growing demand for lithium ion secondary batteries (hereinafter referred to as “batteries”) for use in the driving power sources of those devices and vehicles.
As the batteries used in such applications, a variety of lithium ion secondary batteries such as LiFePO4 have been proposed which use a two-phase coexistence type positive active material in the positive electrode plate (see Patent Documents 1 and 2).